Merge pull request #5 from breez/ok300-add-rev-swap

Add reverse swap section

README.md

@@ -1 +1,8 @@
 # Introduction
+
+The SDK docs are live at [https://sdk-doc.breez.technology]().
+
+
+## Contributions
+
+For syntax and supported features, see [https://rust-lang.github.io/mdBook]().

src/guide/send_onchain.md

@@ -1 +1,51 @@
 # Sending an on-chain transaction (swap-out)
+
+You can send funds from the Breez SDK wallet to an on-chain address as follows.
+
+First, fetch the current reverse swap fees:
+
+```rust,no_run
+let current_fees = sdk.fetch_reverse_swap_fees().await?;
+
+info!("Percentage fee for the reverse swap service: {}", current_fees.fees_percentage);
+info!("Estimated miner fees in sats for locking up funds: {}", current_fees.fees_lockup);
+info!("Estimated miner fees in sats for claiming funds: {}", current_fees.fees_claim);
+```
+
+The reverse swap will involve two on-chain transactions, for which the mining fees can only be estimated. They will happen
+automatically once the process is started, but the last two values above are these estimates to help you get a picture
+of the total costs.
+
+Fetching the fees also tells you what is the range of amounts you can send:
+
+```rust,no_run
+info!("Minimum amount, in sats: {}", current_fees.min);
+info!("Maximum amount, in sats: {}", current_fees.max);
+```
+
+Once you checked the fees are acceptable, you can start the reverse swap:
+
+```rust,no_run
+let destination_address = String::from("bc1..");
+let amount_sat = current_fees.min;
+
+sdk.send_onchain(amount_sat, destination_address, current_fees.fees_hash).await?;
+```
+
+Starting the reverse swap will trigger a HODL invoice payment, which will only be settled if the entire swap completes.
+This means you will see an outgoing pending payment in your list of payments, which locks those funds until the invoice
+is either settled or cancelled. This will happen automatically at the end of the reverse swap.
+
+You can check its status with:
+
+```rust,no_run
+for rs in sdk.in_progress_reverse_swaps().await? {
+    info!("Reverse swap {} in progress, status is {}", rs.id, rs.breez_status);
+}
+```
+
+If the reverse swap is successful, you'll get the on-chain payment on your destination address and the HODL invoice will
+change from pending to settled.
+
+If however something goes wrong at any point in the process, the initial HODL payment will be cancelled and the funds in
+your Breez SDK wallet will be unlocked.